Sorry in advance for the noob question. I bought 16gb (2 x 8gb). I followed the instruction verbatim from OWC site and from Apple site. After removing all three original 1gb sticks, I inserted the first two 8gb sticks into slots 1 & 2 and then in slots 3 & 4 placed the 1gb sticks that came w/ computer originally. Once I turned power on, the light above power button flashing quickly, nothing on screen. What should I do?